A promising new field for information storage uses optical data stored in the form of holograms. Holograms are three dimensional images that can be used to store large amounts of digital data. Holographic storage systems under development are capable of storage densities of tens or hundreds of data bits per .mu.m.sup.2.
Lithium niobate has been studied extensively as an optical storage medium and offers the advantage that data can be written read, erased, and re-written. However, inorganic crystal materials such as lithium niobate are not ideal for creating large data banks. Moreover, this medium tends to be volatile, i.e. the data degrades upon reading. Methods have been developed for making these materials non-volatile, but they require heating the storage medium, or a very high writing flux, either of which limits the usefulness of the material.
More promising, for read-only storage applications, are polymer matrix materials containing monomers and photoinitiators. Irradiation results in polymerization that induces local changes in the refractive index of the polymer body. This approach allows the use of independent chemistries for the matrix material and for the photosensitive material. The matrix can be designed independently for mechanical and thermal stability, and shelf life.
A promising candidate for a high density optical storage medium is Mercapto-Epoxy-Bromo-Styrene (MEBS). See U.S. patent application Ser. No. 09/046822, which is incorporated herein by reference. However, studies have shown that this material, while highly effective as an optical storage medium, has useful but limited shelf life in an uncontrolled, e.g. humid, environment. This polymer, not unlike polymers in general, has a tendency to absorb moisture during storage, which causes the material to swell and undergo refractive index changes in a spatially non-uniform fashion. Since the material is typically placed between glass plates, the non-uniform swelling and/or refractive index change in the polymer diminishes the optical quality of the storage medium. Other polymer materials that may be useful for optical storage are also sensitive to atmospheric conditions that limit shelf life. Accordingly, if these polymer storage media are to be effective for these applications, techniques for improving their shelf life need to be developed.